I. Field of the Invention
The present invention relates generally to medical ventilators.
II. Description of the Prior Art
Medical ventilator systems have been long used to provide supplemental oxygen support to patients unable to breathe normally on their own accord. These previously known medical ventilators typically comprise a source of pressurized oxygen which is fluidly connected to the patient through a fluid conduit.
A variably actuatable valve is connected in series with the fluid conduit to vary the fraction of positive pressure inspired oxygen (FiO2) to the patient. FiO2 will vary between 0.21, in which no supplemental oxygen support is provided to the patient, and 1.0, in which pure oxygen is provided to the patient.
In order to determine the proper FiO2, the arterial oxygen saturation (SpO2) is typically monitored via a pulse oximeter attached to the patient. The SpO2 is ideally in the range of 0.97-1.0 whereas an SpO2 of less than 0.91 is dangerously low. Consequently, the FiO2 should be increased as the SpO2 decreases.
Many of these previously known medical ventilators are manually controlled, i.e. the patient is continuously monitored by medical personnel and the FiO2 adjusted accordingly. Such systems, however, are disadvantageous not only since they require extensive medical attention by medical personnel, but are inherently inaccurate. Such inaccuracies increase the amount of time necessary to wean the patient from the ventilator system.
There have, however, been attempts to automate the adjustment of FiO2 as a function of the patient""s SpO2. Many of these previously known systems, however, merely adjust the amount of FiO2 in preset increments as a function of the value of the SpO2. For example, if the SpO2 falls below a preset threshold, the FiO2 is increased in preset increments until the SpO2 is above the threshold level. Conversely, if the SpO2 increases past a maximum threshold, e.g. 0.99, the FiO2 is decreased in preset increments until the SpO2 is between the upper and lower thresholds.
While these previously known automated ventilation systems have effectively reduced the amount of required medical attention for the patient, they have not significantly reduced the amount of time necessary to wean the patient from the medical ventilator.
The present invention provides a medical ventilator system which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the medical ventilator system of the present invention comprises a source of pressurized oxygen which is fluidly connected to the patient via a fluid conduit or breathing tube. A variably actuatable valve is fluidly connected in series with the conduit so that the FiO2 support for the patient varies as a function of the valve actuation.
The ventilator system further includes a controller for controlling the actuation of the valve and thus the FiO2 support to the patient. The controller is preferably microprocessor based and receives an SpO2 signal from a pulse oximeter attached to the patient. The controller then outputs control signals to the valve to control the valve actuation and thus the FiO2 support to the patient.
In one embodiment of the invention, the controller monitors not only the magnitude of the SpO2 signal, but also the rate of change of the SpO2 signal. The controller then utilizes the magnitude and rate of change of the SpO2 signal to calculate a xcex94FiO2 value, i.e. the amount of change of the FiO2 support to the patient, in accordance with a preset formula.
In a second embodiment of the invention, however, the controller utilizes fuzzy logic in lieu of the preset formula in order to calculate the xcex94FiO2. The fuzzy logic effectively utilizes a lookup table to increase the xcex94FiO2 by a greater amount as the patient""s SpO2 becomes lower.
In practice, the medical ventilator of the present invention not only safely and effectively provides ventilation support for the patient, but also effectively reduces the amount of time required to wean the patient from the ventilator.